We often hear talk (specially in car audio) about certain boxes being RIGHT for certain woofers. Many folks talk like a given woofer wont even play at all if the box size is not exactly perfect!
What is perfect?
Manufacturers often recommend a certain box for their speakers.
Computer box programs can PICK the box size (or tuning) that works best(?) with the woofer if you input the Thiele/Small parameters.
Is the box size the manufacturer recommends perfect? How can it possibly be perfect when they don't even know what kind of car your installing the box into? We all know the car will change the sound (this is called transfer function)! How can they possibly choose the perfect box size? Many times the speaker manufacturers recommendation is chosen not for perfect sound but for an average that might work well in the average car. Many times they might recommend the box that's easiest to build for beginners or small (since many folks like woofs that work in small boxes) or sealed instead of vented because it is less likely for you to blow your speaker in a small sealed box than a large vented box! (if you blow your speaker (a) they might have to replace it. (b) the company might get a reputation for lousy speakers if they blow a lot) Sure, the manufacturers recommendation will probably sound great! But perfect??? Is the manufacturers recommended box size really right for you?
Is the box size provided by computer programs perfect? Again, how can it be unless they take into account the transfer function of the car??? I don't know of a current popular program that does! Most computer programs will calculate a box for you with the lowest response and with the least ripple. In car audio, this many times IS NOT the best! Sometimes (specially in SPL competitions) the ripple the computer program tries to avoid might actually be an SPL or bass boost! Or for an SQ car, a slight ripple (inaudible, an may likely be made up for by the cars transfer function) might get you much deeper bass... Is the computers recommendation the perfect box? Is the computer programs recommended box right for you?
How bout the difference in CUSTOM made boxes vs PREFAB boxes?
Most real car audio enthusiasts would never consider a PREFAB box, we all know the custom built boxes are far superior sounding... BUT ARE THEY REALLY?
From my experience there is a great amount of BADLY BUILT custom boxes being built! Built so badly in fact that for many cases a prefab box would be miles better!
A prefab box could be better than a badly built custom box! I have heard some darned good systems with prefab boxes and some very poor systems with custom built boxes.. It's important if your gonna pay high dollar for an installer to build you a custom box that the installer be good at building boxes or you might just as well have spent your money on a pre-fab and spent the left over money on something else.
PLUS, since we mentioned installers, how many really have any background in speaker design? Many claim to be experts, but in the real world most installers just build the so called custom boxes with no AUDIO PHYSICS in mind. So for a custom box, its important the installer be not only a carpenter but also an expert at loudspeaker box design... Or a pre-fab box might be the better choice! ;-)
And, in reality, there is no PERFECT box, and to really custom build a box to perform as good as possible in a given vehicle it requires huge stacks of expensive test equipment, lots of woodworking tools and saws, and building, testing then rebuilding and retesting, and rebuilding and retesting again and again and again until no more good is achieved. This is done only by a few crazy competition gurus or a few nutty hobbyists, certainly NOT for the average car audio guy, or even the average installer...
So, I think it would be safe to say most so called perfect boxes are no where near perfect, they can all be improved on. And even if they were perfect, putting them in a car will change them, even the direction the box fires in the car can have an effect!
And it makes me laugh when I hear a fellow say something like " the manufacturer recommends 1.5cu ft for this speaker, it wont work in 1.25cu ft!"
Sure it will!
If that's all the space you have,
build it,
play it,
enjoy it!
There are so many variables involved there is a chance the NON-PERFECT box might even sound better than the so called perfect one! Try it ;-)
Enjoy!
Putting a speaker in a vehicle (or room for that matter) will make the speaker sound different. This is caused by reflections, absorptions and resonance's that exist in that car. This change is called the transfer function.
All cars have a transfer function, typically the most noticeable change to speakers when placed in a car is MORE BASS. More bass is inherent because the car is like a box, an enclosed space that promotes reinforcing reflections of the bass sounds (because the bass waves are long enough to be reflected and still be close enough to in phase and reinforce)....
But the transfer function is more than just a change in bass, it also can cause major changes in the midrange speakers because of the major glass surfaces for the sound to bounce off of! Or the high frequency sounds from the tweeters can be absorbed into the headliner or car upholstery (intentionally sound absorbent by the car manufacturer to absorb road noise)...
So, we cant easily change the transfer function, but we can map it, and then build our system to take advantage of our cars transfer function.
To map the transfer function you will need a Speaker box, a CD with test tones or an audio test generator or a pink noise generator and a decibel meter. There are several CDs available with test tones, I prefer the tone generator but they are fairly expensive and hard to find an install shop with one, pink noise is OK but pink noise generators are probably just as hard to find as audio generators. And for a decibel meter Radio shack sells one for about $30 that will work. Oh, and a piece of graph paper to write down your results.
First, lets map the speaker box. Take your speaker box outdoors in the back yard and aim it away from the house to minimize reflections, hang the SPL meter or microphone for it a few meters in front of the speaker box. Fire up your test tones and set the volume level where the SPL meter gets a reading on most of your test tones (if the low ones don't register don't worry), but not too loud, we don't want to damage the test speaker! Now without touching the volume control, run your test tones and write down on your graph paper the SPL at each tone. You can even make a graph on the graph paper if you want to.
Your results is the frequency response of your test speaker!
Lets put this box in the car and do the test again and see what changes!
Set the test speaker in a nice location, preferably close to where the real speakers will go later. Hang the microphone in the center of the car near where your ears would be if you were driving, and run through the test tones again, reading the SPL meter and writing down the results on the graph paper.
When you done, subtract the back yard numbers from the in car numbers for each frequency and write down your results. For instance, if you had 90dB at 120Hz in the back yard and 95dB in the car then (95-90=5) write down 120Hz=+5dB, and do this for every frequency you mapped. Some frequencies may have negative numbers, this is OK... When your done, you should have a series of frequencies=numbers something like this: 20=+4, 40=+6, 80=+12, 120=+3, 200=0, 400=-3, 600=-4, and so on...
This is your transfer function, you can now look at any frequency and tell what
your car is going to do to ANY SPEAKER you install.
Simple....
All cars have a transfer function, typically the most noticeable change to speakers when placed in a car is MORE BASS. More bass is inherent because the car is like a box, an enclosed space that promotes reinforcing reflections of the bass sounds (because the bass waves are long enough to be reflected and still be close enough to in phase and reinforce)....
But the transfer function is more than just a change in bass, it also can cause major changes in the midrange speakers because of the major glass surfaces for the sound to bounce off of! Or the high frequency sounds from the tweeters can be absorbed into the headliner or car upholstery (intentionally sound absorbent by the car manufacturer to absorb road noise)...
So, we cant easily change the transfer function, but we can map it, and then build our system to take advantage of our cars transfer function.
To map the transfer function you will need a Speaker box, a CD with test tones or an audio test generator or a pink noise generator and a decibel meter. There are several CDs available with test tones, I prefer the tone generator but they are fairly expensive and hard to find an install shop with one, pink noise is OK but pink noise generators are probably just as hard to find as audio generators. And for a decibel meter Radio shack sells one for about $30 that will work. Oh, and a piece of graph paper to write down your results.
First, lets map the speaker box. Take your speaker box outdoors in the back yard and aim it away from the house to minimize reflections, hang the SPL meter or microphone for it a few meters in front of the speaker box. Fire up your test tones and set the volume level where the SPL meter gets a reading on most of your test tones (if the low ones don't register don't worry), but not too loud, we don't want to damage the test speaker! Now without touching the volume control, run your test tones and write down on your graph paper the SPL at each tone. You can even make a graph on the graph paper if you want to.
Your results is the frequency response of your test speaker!
Lets put this box in the car and do the test again and see what changes!
Set the test speaker in a nice location, preferably close to where the real speakers will go later. Hang the microphone in the center of the car near where your ears would be if you were driving, and run through the test tones again, reading the SPL meter and writing down the results on the graph paper.
When you done, subtract the back yard numbers from the in car numbers for each frequency and write down your results. For instance, if you had 90dB at 120Hz in the back yard and 95dB in the car then (95-90=5) write down 120Hz=+5dB, and do this for every frequency you mapped. Some frequencies may have negative numbers, this is OK... When your done, you should have a series of frequencies=numbers something like this: 20=+4, 40=+6, 80=+12, 120=+3, 200=0, 400=-3, 600=-4, and so on...
This is your transfer function, you can now look at any frequency and tell what
your car is going to do to ANY SPEAKER you install.
Simple....
WIRE 1
This POS+ wire connects the two batteries' positive posts. This wire allows the rear battery to receive the charge from the alternator, just like the front battery receives. Without this wire, the rear battery would not maintain a charge.
WIRE 1 should be at least 1/0 awg wire. The reason why is that when batteries are connected together, they will instantly equalize in voltage. This can be hundreds of amps of current that is passed. Anything smaller than 1/0 awg wire is likely to be too small to transfer these high currents.
If you intend on pulling more than 300A of current across WIRE 1, you should add an additional run of 1/0 awg for each additional 300A of current you intend on pulling. So if you plan on pulling 600A, you would need two runs of 1/0 awg minimum. The more runs of 1/0 awg you have, the less voltage you can expect to lose due to resistance.
WIRE 2
This POS+ wire connects your amp(s) to your rear battery. This wire should be sized based on the input of your amp(s). If your amp has a 4 awg input, this should be a 4 awg wire. If your amp accepts 1/0 wire, then this should be a 1/0 awg wire.
If you decide that it is better for your setup, you can choose to use a distribution block between the battery's POS+ post and the amps' POS+ inputs. Some people prefer to use a distro block, but it is easier in my mind to simply run the wire directly from the POS+ post to each amp, in effect using the battery as the distro block. There is no right or wrong here, it is up to you to decide.
WIRE 3
This NEG- wire connects the two batteries' negative posts. This wire size should be identical to the size (and quantity) of WIRE 1. So, if you have two runs of 1/0 awg being used for WIRE 1, then you will need two runs of 1/0 awg for WIRE 3 as well.
Some people will argue that using the chassis instead of wire for your NEG- (grounds) connections is fine, but when you have multiple batteries, that is no longer going to be sufficient in most cases. If your car does not have one solid piece of steel running the length of the car, then you will have multiple pieces of steel that are welded together. Steel, as you well know, is a poor conductor when compared to copper (or other highly conductive metals). The conductivity of steel is highly reduced when welded together with another piece of steel. Imagine the weld as a speed bump.
Now the other issue here that is frequently overlooked is that as you begin to draw more current over a conductor, the impedance will actually rise. So simply measuring the resistance of your chassis without a current draw is pointless.
WIRE 4
This NEG- wire is to connect the NEG- connections on your amp to the NEG- post of the rear battery. It is important that this wire matches the size (and quantity) of WIRE 2. Again, just like with WIRE 2, the size of this wire should be determined by your amps' inputs.
Some people again would tell you to not wire this to the battery, but instead to the chassis. This would be OK if you did not have a rear battery and you had a very small amp. But since this discussion is assuming the rear battery is installed, you need to wire the NEG- connection for the amp directly to the battery.
WIRE 5
These wires are to ground each battery to the chassis for devices that may not have a NEG- wire running directly, but are still pulling power from the battery. A good example would be lights or other chassis grounded devices.
One last wire that is not shown, but would fall under the WIRE 5 category would be a wire from the front battery NEG- post to the engine block. This in essence would be the NEG- wire to the alternator, since the engine block is electrically connected to the alternator. If your alternator in fact has a NEG- post, of course the wire should connect there and not at the engine block.
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And now on to the fuses. Each fuse shown above serves a specific purpose. There are some people who live life on the edge and feel they are a waste of money. There are others who claim that they affect voltages in your vehicle. I am neither of these. I like feeling safe and secure knowing that my electrical system is protected by a fuse. These fuses will not only protect you from improper wiring, but also protect you in case of an accident that shorts out a POS+ wire. Also, good ANL fuses have very little added resistance, so the voltage drop across a fuse is usually not measurable.
FUSE A
This fuse should be located as close to the POS+ post of the front battery as possible. This fuse should be rated to match the current rating of WIRE 1. If you are using a single run of 1/0 awg wire for WIRE 1 and it is rated up to 300A, then FUSE A should be rated at the same 300A.
What FUSE A does is protect your wire from transferring more current (amps) than it is rated for. In the case of a short circuit in the middle on WIRE 1, the front battery will try to push all of it's energy through WIRE 1 to that short. When this happens, the amount of current will exceed the fuse value and cause the fuse to blow. When the fuse blows, the short is alleviated and no more current will pass along WIRE 1 from the front battery.
If the fuse would not have blown, the excessive amount of current would have exceeded the capacity of WIRE 1, which would have caused a fire.
FUSE B
This fuse does the exact same thing as FUSE A with the exception that it protects WIRE 1 from the current coming from the rear battery. If WIRE 1 were to be shorted, there is a potential for energy to flow from both batteries. A fuse on both ends of WIRE 1 is essential. Again it should be located as close to the POS+ post of the rear battery as possible.
And there is no reason to use only one of these two fuses here on WIRE 1. If you don't have both FUSE A AND FUSE B, then you are not protected from a short. So don't think that having one of the two is going to help you. Unless you have both, you are not protected at all.
FUSE C
This fuse is intended to protect WIRE 2 from to much current. Just as with WIRE 1 and FUSE A & B, you are going to match FUSE C with the current rating of WIRE 2. So if your amp accepts 4 awg wire, WIRE 2 should be 4 awg. If your 4 awg wire is rated up to 125A, then FUSE C should be 125A.
Tuning of a ported subwoofer box is determined by a combination of port area, port length, and net volume of the subwoofer box. Tuning changes the frequency at which the frequency response peaks (is loudest) and can change the way a subwoofer box sounds in your setup. Your tuning choice will be determined by the goal of your system install.
If you're looking to achieve an SPL setup your car (getting as loud as possible), you'll want to tune fairly high. High tuning for SPL is usually somewhere around 45Hz or possibly higher. At this high of tuning, the sound quality will not be very good, but it will be louder than if you were to tune low. A SQ (sound quality) based setup will call for a tuning fairly low - even down around 25Hz. This will also allow you to hit the ultra-low notes with your system. Lower-tuned boxes produce better sound quality, more like a sealed box. The downside to lower tuning is that it flattens the frequency response, which will cause the box to lack the boost around the tuning frequency.
To achieve a good mix between SPL and SQ with a ported box, we have found that it's good to be in the lower 30's for tuning. If you tune up around 35Hz, you'll get a fair amount of SPL out of the box and still have fairly good sound quality. If you tune closer to 30, the box will yield better sound quality but have a little less output than the 35Hz. A range between 30 and 35 Hz is generally good for most general setups.
If you want SPL, tune high. If you want SQ, tune low. If you want somewhere in-between the two, we have found a good tuning is right at 33Hz. This is why we default the port tuning to 33Hz on our customization pages for our ported enclosures. When choosing a ported subwoofer box, the freedom to tune the enclosure is a great way to get your system sounding the way you want it to sound.
Parallel/Parallel DVC Subwoofer Wiring:
* Four 4 ohm DVC subwoofers = 0.5 ohm amplifier load
* Four 8 ohm DVC subwoofers = 1 ohm amplifier load
Series/Parallel DVC Subwoofer Wiring:
* Four 1 ohm DVC subwoofers = .5 ohm amplifier load
* Four 2 ohm DVC subwoofers = 1 ohm amplifier load
* Four 4 ohm DVC subwoofers = 2 ohm amplifier load
* Four 8 ohm DVC subwoofers = 4 ohm amplifier load
Parallel/Series DVC Subwoofer Wiring:
* Four 1 ohm DVC subwoofers = 2 ohm amplifier load
* Four 2 ohm DVC subwoofers = 4 ohm amplifier load
* Four 4 ohm DVC subwoofers = 8 ohm amplifier load
* Four 8 ohm DVC subwoofers = 16 ohm amplifier load
Parallel/Parallel DVC Subwoofer Wiring:
* Three 4 ohm DVC subwoofers = 0.67 ohm amplifier load
* Three 8 ohm DVC subwoofers = 1.33 ohm amplifier load
Series/Parallel DVC Subwoofer Wiring:
* Three 1 ohm DVC subwoofers = 0.67 ohm amplifier load
* Three 2 ohm DVC subwoofers = 1.34 ohm amplifier load
* Three 4 ohm DVC subwoofers = 2.67 ohm amplifier load
* Three 8 ohm DVC subwoofers = 5.36 ohm amplifier load
Parallel/Series DVC Subwoofer Wiring:
* Three 1 ohm DVC subwoofers = 1.125 ohm amplifier load
* Three 2 ohm DVC subwoofers = 2.18 ohm amplifier load
* Three 4 ohm DVC subwoofers = 2.45 ohm amplifier load
* Three 8 ohm DVC subwoofers = 2.82 ohm amplifier load
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